Multisectorial changes in the ciliary muscle during accommodation measured with high-resolution optical coherence tomography / Alterações multissetoriais no músculo ciliar durante a acomodação com uma tomografía de coerência óptica de alta resolução

ABSTRACT Purpose: To measure changes in the anterior ciliary muscle during accommodation at the nasal, superior, temporal, and inferior sectors by means of an anterior chamber optical coherence tomographer, and correlate them with vergence changes. Methods: Twenty-four subjects with healthy, phakic eyes, whose mean age was 27.1 ± 8.9 years, underwent measurement with an anterior chamber optical coherence tomographer. The anterior ciliary muscle was measured at the nasal, temporal, superior, and inferior sectors for 0, -1, -2, and -3 D of vergence. A linear model was used to assess the correlation of each eye parameter with the accommodative demand. Results: The anterior ciliary muscle area significantly increased with accommodation for each sector, with a maximum increase of about 30% for the nasal-temporal sectors and about 25% for the inferior-temporal sectors. The linear model showed a tendency toward a positive relationship between change in the ciliary muscle area of each sector and vergence. Conclusion: The anterior ciliary muscle area tends to increase with accommodation, although the increase has been shown to be symmetric between the pair sectors superior-nasal and inferior-temporal. These results may help to increase understanding of accommodation biometry and biomechanics.

RESUMO Objetivo: Medir as alterações do músculo ciliar anterior durante a acomodação nos setores nasal, superior, temporal e inferior, através de um tomógrafo de coerência óptica de câmara anterior, e correlacioná-las com alterações de vergência. Métodos: Vinte e quatro indivíduos com olhos saudáveis e fácicos, com idade média de 27,1 ± 8,9 anos, foram submetidos à medida com um tomógrafo de coerência óptica de câmara anterior. O músculo ciliar anterior foi medido nos setores nasal, temporal, superior e inferior para 0, -1, -2 e -3D de vergência. Um modelo linear foi utilizado para avaliar a correlação de cada parâmetro do olho com a demanda acomodativa. Resultados: A área do músculo ciliar anterior aumentou significativamente com a acomodação em cada setor, com um aumento máximo foi de cerca de 30% para os setores naso-temporais, e cerca de 25% para os inferiores-temporais. O modelo linear mostrou uma tendência para uma relação positiva entre a alteração da área do músculo ciliar de cada setor e a vergência. Conclusão: A área do músculo ciliar anterior tende a aumentar com a acomodação, embora o aumento tenha se mostrado simétrico entre os setores superior-nasal e inferior-temporal. Estes resultados podem ajudar a aumentar a compreensão da biometria e biomecânica da acomodação.

Effect of age in the ciliary muscle during accommodation: Sectorial analysis / Efecto de la edad en el músculo ciliar durante la acomodación: análisis sectorial

Purpose: To compare changes in the ciliary muscle area at different sectors between pre-presbyopic and presbyopic eyes during accommodation by means of an anterior segment optical coherence tomographer (OCT). Methods: The anterior ciliary muscle area was measured in 20 healthy and phakic pre-presbyopic eyes, whose mean age was 23.3 ± 4.4 years, and in 20 healthy and phakic presbyopic eyes, whose mean age was 46.5 ± 5.2 years. The relative change in the cross-sectional area of the ciliary muscle was measured at the nasal, inferior, and temporal sectors between 0 and - 3 D of vergence, in -1 D step. A linear model was used to assess the correlation of each eye parameter with the accommodative demand. Results: Each population group showed a significant increase in the anterior ciliary muscle area for each sector. The maximum increase in the ciliary muscle area within the pre-presbyopic group was about 30%, and for the presbyopic one was about 25%. At the same time, it was obtained that the larger the vergence, the larger the variability. Furthermore, the linear model showed a positive tendency between the change in the ciliary muscle area of each sector and the vergence for both population groups, which coefficient of determination was in all cases greater than 0.93. Conclusion: The anterior ciliary muscle area tends to increase with accommodation. The presbyopic nasal, inferior, and temporal ciliary muscle seem to have the same contractile capability as the young presbyopic ciliary muscle. These results might help to increase the evidences in the knowledge regarding the modern understanding of accommodation biometry and biomechanics

Objetivo: Comparar los cambios en el área del músculo ciliar en diferentes sectores entre ojos con pre-presbicia y presbicia durante la acomodación, por medio de un tomógrafo de coherencia óptica (OCT) de segmento anterior. Métodos: Se midió el área del músculo ciliar en 24 ojos sanos fáquicos y con pre-presbicia, con edad media de 23,3 ± 4,4 años, y en 20 ojos sanos fáquicos y con presbicia, con edad media de 46,5 ± 5,2 años. El cambio relativo en el área transeccional del músculo ciliar se midió en los sectores nasal, inferior y temporal entre 0 y -3 D de vergencia, en pasos de -1D. Se utilizó un modelo lineal para valorar la correlación de cada parámetro del ojo con la demanda acomodativa. Resultados: Cada grupo de población reflejó un incremento significativo en el área del músculo ciliar para cada sector. El incremento máximo en el área del músculo ciliar en el grupo de pre-presbicia fue de alrededor del 30%, y para el grupo de presbicia de cerca del 25%. También se observó que cuanto mayor era la vergencia, mayor era la variabilidad. Además, el modelo lineal reflejó una tendencia positiva entre el cambio en el área del músculo ciliar de cada sector y la vergencia para ambos grupos de población, cuyo coeficiente de determinación fue en todos los casos superior a 0,93. Conclusión: El área anterior del músculo ciliar tiende a incrementarse con la acomodación. El músculo ciliar en los sectores nasal, inferior y temporal en la presbicia parece tener la misma capacidad contráctil que el músculo ciliar pre-presbicia. Estos resultados podrían ayudar a incrementar las evidencias en el conocimiento relativo a la comprensión moderna de la biometría de acomodación y la biomecánica

Influence of contrast polarity on the accommodative response / Influencia de la polaridad de contraste en la respuesta acomodativa

Purpose: To assess the changes in the accommodative response of the eye while reading a text under different contrast polarity conditions: black letters on white background (BoW condition) and white letters on black background (WoB condition). Methods: Eighteen subjects with ages ranging from 21 to 41 years participated in this experimental study. The accommodative response (AR) of the eye while reading a text with BoW or WoB contrast polarity was obtained objectively with an adaptive optics system that corrected all aberrations but subject's own. Two different letter sizes (visual acuity conditions), shown on a microdisplay, were tested. The AR of each eye was measured with its natural pupil diameter at 0-3D of accommodative demand from the far point of the eye, with a step of 0.5D. The slope of the stimulus-response curve was calculated for each subject and condition. Results: The averaged maximum pupil size was bigger for reverse (WoB) than for normal (BoW) contrast with statistical significance. The slopes for the ARs of the four conditions were not significantly different from each other. Conclusions: Contrast polarity does not seem to influence the accommodative response when reading text from an electronic microdisplay

Objetivo: Evaluar los cambios de la respuesta acomodativa del ojo al leer un texto en diferentes condiciones de polaridad de contraste: letras negras sobre fondo blanco (condición BoW) y letras blancas sobre fondo negro (condición WoB). Métodos: En este estudio experimental participaron dieciocho sujetos de edades comprendidas entre 21 y 41 años. Se obtuvo objetivamente la respuesta acomodativa (AR) del ojo al leer un texto con polaridad de contraste BoW o WoB con un sistema de óptica adaptativa que corregía todas las aberraciones salvo las propias del sujeto. Se estudiaron dos tamaños de letra diferentes (condiciones de agudeza visual), mostrados en una micropantalla. Se midió la AR de cada ojo con su diámetro de pupila natural con 0 a 3 D de demanda acomodativa desde el punto remoto del ojo, en intervalos de 0,5 D. Se calculó la pendiente de la curva estímulo-respuesta para cada sujeto y condición. Resultados:El tamaño máximo medio de la pupila fue mayor para el contraste inverso (WoB) que para el normal (BoW), con significación estadística. Las pendientes de las AR para las cuatro condiciones no difirieron significativamente entre ellas. Conclusiones: La polaridad de contraste no parece influir en la respuesta acomodativa al leer un texto en una micropantalla electrónica

Effect of contact lenses on ocular biometric measurements based on swept-source optical coherence tomography / Efeito de lentes de contato em um biômetro ocular baseado na tomografia de coerência óptica de varredura

ABSTRACT Purpose: To determine the reliability of swept- source optical coherence tomography in cases in which soft contact lenses cannot be removed when acquiring biometric measurements. Methods: Eight subjects were included and only one eye per participant was analyzed. Each eye was measured six times by swept-source optical coherence tomography with the IOLMaster 700 instrument (Carl Zeiss Meditec, Jena, Germany). Axial length, central corneal thickness, anterior chamber depth, lens thickness, and keratometric measurements were evaluated for the naked eye and while wearing soft contact lenses of three different powers (-1.5, -3.0, and +2.0 D). Results: There were statistically significant changes in axial length, central corneal thickness, anterior chamber depth, and keratometric measurements with soft contact lenses as compared to the naked eye (p<0.001). However, there were no significant differences in lens thickness outcomes between the naked eye and while wearing the three soft contact lenses (p>0.5). The changes in axial length, central corneal thickness, and anterior chamber depth were lens-specific and dependent on the thickness of the lens used. Conclusions: Sept-source optical coherence tomography based lens thickness measurements while wearing soft contact lenses are comparable to those of the naked eye. However, the thickness and the optical design of the soft contact lens may lead to significant differences in the axial lengh, central corneal thickness, anterior chamber deph, and keratometric measurements.

RESUMO Objetivo: Determinar a confiabilidade da tomografia de coerência óptica de varredura em casos especiais em que lentes de contato gelatinosas não podem ser removidas ao realizar medições biométricas. Métodos: Oito indivíduos foram incluídos e apenas um olho por participante foi analisado. Cada olho foi medido seis vezes por tomografia de coerência óptica de varredura com o instrumento IOLMaster 700 (Carl Zeiss Meditec, Jena, Alemanha). O comprimento axial, a espessura central da córnea, a profundidade da câmara anterior, a espessura da lente e as medidas ceratométricas foram avaliados a olho nu e enquanto usavam lentes de contato gelatinosas de três diferentes potências (-1,5, -3,0 e +2,0 D). Resultados: Houve alterações significativas no comprimento axial, espessura central da córnea, profundidade da câmara anterior e medidas ceratométricas com as lentes de contato gelatinosas em comparação com as a olho nu (p<0,001). No entanto, não houve diferenças significativas nos resultados de espessura do cristalino entre o olho nu e enquanto usava as três lentes de contato gelatinosas (p>0,5). As alterações de comprimento axial, espessura central da córnea e profundidade da câmara anterior foram específicas da lente e dependentes da espessura da lente usada. Conclusões: As medições da espessura da lente baseadas na tomografia de coerência óptica da Sept-source, enquanto usam lentes de lentes de contato gelatinosas, são comparáveis às do olho nu. Entretanto, a es pessura e o desenho óptico da lente de contato gelatinosa podem levar a diferenças significativas no comprimento axial, na espessura central da córnea, na profundidade da câmara anterior e nas medidas ceratométricas.

Effect of contact lenses on ocular biometric measurements based on swept-source optical coherence tomography.

PURPOSE: To determine the reliability of swept- source optical coherence tomography in cases in which soft contact lenses cannot be removed when acquiring biometric measurements. METHODS: Eight subjects were included and only one eye per participant was analyzed. Each eye was measured six times by swept-source optical coherence tomography with the IOLMaster 700 instrument (Carl Zeiss Meditec, Jena, Germany). Axial length, central corneal thickness, anterior chamber depth, lens thickness, and keratometric measurements were evaluated for the naked eye and while wearing soft contact lenses of three different powers (-1.5, -3.0, and +2.0 D). RESULTS: There were statistically significant changes in axial length, central corneal thickness, anterior chamber depth, and keratometric measurements with soft contact lenses as compared to the naked eye (p<0.001). However, there were no significant differences in lens thickness outcomes between the naked eye and while wearing the three soft contact lenses (p>0.5). The changes in axial length, central corneal thickness, and anterior chamber depth were lens-specific and dependent on the thickness of the lens used. CONCLUSIONS: Sept-source optical coherence tomography based lens thickness measurements while wearing soft contact lenses are comparable to those of the naked eye. However, the thickness and the optical design of the soft contact lens may lead to significant differences in the axial lengh, central corneal thickness, anterior chamber deph, and keratometric measurements.

Multisectorial changes in the ciliary muscle during accommodation measured with high-resolution optical coherence tomography.

PURPOSE: To measure changes in the anterior ciliary muscle during accommodation at the nasal, superior, temporal, and inferior sectors by means of an anterior chamber optical coherence tomographer, and correlate them with vergence changes. METHODS: Twenty-four subjects with healthy, phakic eyes, whose mean age was 27.1 ± 8.9 years, underwent measurement with an anterior chamber optical coherence tomographer. The anterior ciliary muscle was measured at the nasal, temporal, superior, and inferior sectors for 0, -1, -2, and -3 D of vergence. A linear model was used to assess the correlation of each eye parameter with the accommodative demand. RESULTS: The anterior ciliary muscle area significantly increased with accommodation for each sector, with a maximum increase of about 30% for the nasal-temporal sectors and about 25% for the inferior-temporal sectors. The linear model showed a tendency toward a positive relationship between change in the ciliary muscle area of each sector and vergence. CONCLUSION: The anterior ciliary muscle area tends to increase with accommodation, although the increase has been shown to be symmetric between the pair sectors superior-nasal and inferior-temporal. These results may help to increase understanding of accommodation biometry and biomechanics.

Influence of contrast polarity on the accommodative response.

PURPOSE: To assess the changes in the accommodative response of the eye while reading a text under different contrast polarity conditions: black letters on white background (BoW condition) and white letters on black background (WoB condition). METHODS: Eighteen subjects with ages ranging from 21 to 41 years participated in this experimental study. The accommodative response (AR) of the eye while reading a text with BoW or WoB contrast polarity was obtained objectively with an adaptive optics system that corrected all aberrations but subject's own. Two different letter sizes (visual acuity conditions), shown on a microdisplay, were tested. The AR of each eye was measured with its natural pupil diameter at 0-3D of accommodative demand from the far point of the eye, with a step of 0.5D. The slope of the stimulus-response curve was calculated for each subject and condition. RESULTS: The averaged maximum pupil size was bigger for reverse (WoB) than for normal (BoW) contrast with statistical significance. The slopes for the ARs of the four conditions were not significantly different from each other. CONCLUSIONS: Contrast polarity does not seem to influence the accommodative response when reading text from an electronic microdisplay.

Effect of age in the ciliary muscle during accommodation: Sectorial analysis.

PURPOSE: To compare changes in the ciliary muscle area at different sectors between pre-presbyopic and presbyopic eyes during accommodation by means of an anterior segment optical coherence tomographer (OCT). METHODS: The anterior ciliary muscle area was measured in 20 healthy and phakic pre-presbyopic eyes, whose mean age was 23.3±4.4 years, and in 20 healthy and phakic presbyopic eyes, whose mean age was 46.5±5.2 years. The relative change in the cross-sectional area of the ciliary muscle was measured at the nasal, inferior, and temporal sectors between 0 and -3 D of vergence, in -1 D step. A linear model was used to assess the correlation of each eye parameter with the accommodative demand. RESULTS: Each population group showed a significant increase in the anterior ciliary muscle area for each sector. The maximum increase in the ciliary muscle area within the pre-presbyopic group was about 30%, and for the presbyopic one was about 25%. At the same time, it was obtained that the larger the vergence, the larger the variability. Furthermore, the linear model showed a positive tendency between the change in the ciliary muscle area of each sector and the vergence for both population groups, which coefficient of determination was in all cases greater than 0.93. CONCLUSION: The anterior ciliary muscle area tends to increase with accommodation. The presbyopic nasal, inferior, and temporal ciliary muscle seem to have the same contractile capability as the young presbyopic ciliary muscle. These results might help to increase the evidences in the knowledge regarding the modern understanding of accommodation biometry and biomechanics.

Ocular biometric changes with different accommodative stimuli using swept-source optical coherence tomography.

PURPOSE: To evaluate ocular biometric changes with different accommodative stimuli using a new swept-source optical biometer. METHODS: Only the right eye was analyzed. Each subject was measured six times with the IOLMaster 700 swept-source optical biometer (Carl Zeiss Meditec, Jena, Germany) with the subject looking at the stimulus shown by the instrument and with the subject looking at a target placed outside the instrument at 0D of vergence. Axial length (AL), anterior chamber depth (ACD), central corneal thickness (CCT), lens thickness (LT), white-to-white (WTW), and keratometry readings (K1 and K2) were evaluated in both cases. To assess if the changes found may affect the intraocular (IOL) power calculation for surgical applications, we have applied some formulae, using the software provided by the optical biometer manufacturer, to the ocular parameters found in both situations for three different types of IOLs. RESULTS: No statistically significant differences were found for AL, CCT, WTW, K1 and K2 between the subject looking at the stimulus of the biometer and looking at the outside target at 0D of vergence (p > 0.05). However, the measurement of ACD revealed a statistically significant reduction of 20 microns (p = 0.03) and, on the contrary, LT increased significantly 30 microns (p = 0.02). ACD and LT changes were highly correlated (R2 = 0.91). As for the IOL power calculation, in all cases, the mean change was lower than 0.25 D both for IOL power selection and residual refraction. CONCLUSIONS: Although ACD and LT change significantly with different accommodative stimuli measured by swept-source optical biometry, these changes are not clinically relevant.

Repeatability assessment of biometric measurements with different refractive states and age using a swept-source biometer.

BACKGROUND: We aim to assess if refractive error or age may influence the repeatability of measurements using a swept-source biometer. METHODS: A total of 61 subjects were evaluated with IOLMaster 700 acquiring measurements of axial length (AL), central corneal thickness (CCT), white-to-white distance (WTW), anterior aqueous depth (AQD), lens thickness (LT), and keratometry (K) readings. Repeatability was evaluated classifying the sample according to the refractive state and age by the calculation of the within-subject standard deviation (Sw), coefficient of repeatability, and intraclass correlation coefficient. RESULTS: Very similar Sw was acquired among groups for AL, CCT, and WTW. Differences found for AQD, LT, keratometry and astigmatism among refractive and age groups were not clinically significant. Refractive groups obtained a Sw for AQD between 0.016 and 0.026, while for LT was between 0.023 and 0.029 mm. Besides, Sw showed values from 0.014 to 0.029 mm for keratometry. Age groups obtained a Sw of 0.025 and 0.016 mm for AQD, and 0.029 and 0.018 mm for LT, respectively. Sw was 0.019 vs 0.018 mm for K1, 0.014 vs 0.031 mm for K2. CONCLUSIONS: IOLMaster 700 showed good repeatability for biometric and keratometric parameters in eyes classified according to their refractive error or age.

Repeatability of in-vitro optical quality measurements of intraocular lenses with a deflectometry technique effect of the toricity.

AIM: To evaluate the repeatability of an optical device for measuring the Zernike coefficients of toric intraocular lenses (IOLs) and assess whether its toricity has any impact in its repeatability. METHODS: An experienced technician used the NIMO TR1504 to measure the Zernike coefficients 30 times for an aperture of 4.50 mm for all lenses included. The IOLs included were divided into two group: toric and non-toric ones. The cylindrical powers of the toric lenses included in the present study were 1.00, 1.50, 2.25, 3.00 and 3.75 D. Finally, the repeatability of the NIMO TR1504 was described in terms of within subject standard deviation (Sw) and repeatability limit. RESULTS: The Sw was smaller than 0.011 µm for both lens groups and all Zernike coefficients, and the difference between both groups was smaller than 0.004 µm for all Zernike coefficients. Regarding the repeatability limit, this value was smaller than 0.025 µm for the toric lens group, and smaller than 0.031 µm for the non-toric lens one for all Zernike coefficients. Furthermore, the maximum difference between both lens groups was 0.010 µm. CONCLUSION: The repeatability of the NIMO TR1504 to measure the optical quality is high and independent of the lens toricity. These results reflect that this system is robust and could be used to measure the in-vitro optical quality of either toric or non-toric IOLs.

Schematic eye models to mimic the behavior of the accommodating human eye.

A simplified version of the human eye is known as a schematic eye model. Since the first attempts in the middle of the 19th century, numerous approaches describing new schematic eye models have been introduced. Some are able to describe the accommodation ability of the human eye. Accommodated schematic eyes could be of great interest because they explain the functionality of the human eye and they are easy to use for research purposes. Purposes include the design and testing of multifocal ophthalmic intraocular lenses, the evaluation of the effect of optical aberrations on retinal image quality, and the study of the optical performance of the eye at different distances after some refractive surgical procedures. This paper reviews and summarizes the most important features and details of accommodated schematic eye models that have been proposed in the past years.

Agreement of white-to-white measurements with the IOLMaster 700, Atlas 9000, and Sirius systems.

BACKGROUND: Current advances in ocular surgery require the evaluation of differences in automated white-to-white (WTW) measurements between systems. We aim to analyze three different commonly used devices in clinical practice: the IOLMaster 700, the Atlas 9000, and the Sirius. METHODS: Ninety right eyes of ninety healthy subjects were included. Measurements of WTW distances were taken with each device for all subjects in the same session and by the same observer. Statistical comparison was carried out by means of the rANOVA procedure and the Bonferroni post-hoc test. In addition, the Bland-Altman analysis was applied in order to perform pairwise comparisons. RESULTS: Average WTW values obtained by the IOLMaster 700, the Atlas 9000, and the Sirius devices were 12.18 ± 0.40-mm, 12.32 ± 0.37-mm and 11.90 ± 0.37-mm, respectively. There were statistically significant differences in all pairwise comparisons. Mean differences revealed that the Atlas 9000 provided the highest WTW values, followed by the IOLMaster 700 values and finally by the Sirius results, which had the lowest values. The limits of agreement obtained in all pairwise comparisons were wide, with a range between 0.64 and 0.75 mm. CONCLUSIONS: According to our results, these three devices should not be used interchangeably for WTW diameter measurements during the clinical practice.

Accommodative stimulus-response curves to low-pass filtered natural images.

PURPOSE: To assess how the monocular steady-state accommodative stimulus-response curve is modified when viewing low-pass filtered natural images. METHODS: Eighteen adult subjects participated in the study. The accommodative stimulus-response curve was objectively assessed by means of a Hartmann-Shack wavefront sensor. Measurements were taken at different accommodative demands. Target images were low-pass filtered versions of a natural image that were obtained applying different digital spatial filters that limited the spatial frequency content of the natural image. Cutoff spatial frequencies were set at 30, 21, and 15 cycles per degree (cy/deg). RESULTS: Mean data obtained for each target were fitted to linear models. For the low-pass filtered natural image with a cutoff spatial frequency at 30 cy/deg, the slope for the averaged stimulus-response curve was 0.614, while the slopes obtained for the other two low-pass filtered images corresponding to cutoff frequencies at 21 and 15 cy/deg were 0.613 and 0.619, respectively (p < 0.01). The determination coefficient was R2 ≥ 0.988 for all targets. An ANCOVA analysis revealed that these slopes were not significantly different from each other (p = 0.82). Additionally, accommodative error indexes were obtained to measure both the discrepancy between the regression lines and the ideal lines and the degree of correlation between the stimulus and the response. CONCLUSIONS: Our study reveals that the low and middle spatial frequencies (< 15 cy/deg) are the most important to guide to the needed levels the accommodative response to natural images.

In vitro optical quality of monofocal aspheric toric intraocular lenses: effect of cylindrical power.

PURPOSE: To assess the in vitro optical quality of monofocal aspheric toric intraocular lenses (IOLs) as a function of the cylindrical power. METHODS: The in vitro optical quality of the AcrySof IQ Toric IOLs SN6AT2, SN6AT3, SN6AT4, SN6AT5 and SN6AT6 (Alcon Laboratories Inc., Forth Worth, TX, USA) was assessed with an instrument conceived for measuring Zernike's coefficients at 3.0- and 5.0-mm apertures. As a reference, the aspheric monofocal lens AcrySof IQ Aspheric SN60WF (Alcon Laboratories Inc., Forth Worth, TX, USA) was also measured. The area of visibility and cut-off frequency were used to describe the modulation transfer function (MTF) of each lens; meanwhile, the light in the bucket and the diameter of a circular area centred on the point-spread function (PSF) peak that captures 50% of the light energy were used to describe the PSF of each lens. Finally, an image simulation was computed from the Zernike values with reference purposes. RESULTS: Small differences were found on the metrics used for describing the MTF and PSF of the lenses at both tested apertures, but these were not statistically significant (p > 0.05). Furthermore, the image simulation showed that these differences would not have clinical relevance at all. CONCLUSIONS: The optical performance of the AcrySof IQ toric IOLs in terms of MTF and PSF is good and seems to be independent of the cylindrical power and similar to a non-toric aspheric lens.

Amplitude, Latency, and Peak Velocity in Accommodation and Disaccommodation Dynamics.

The aim of this work was to ascertain whether there are differences in amplitude, latency, and peak velocity of accommodation and disaccommodation responses when different analysis strategies are used to compute them, such as fitting different functions to the responses or for smoothing them prior to computing the parameters. Accommodation and disaccommodation responses from four subjects to pulse changes in demand were recorded by means of aberrometry. Three different strategies were followed to analyze such responses: fitting an exponential function to the experimental data; fitting a Boltzmann sigmoid function to the data; and smoothing the data. Amplitude, latency, and peak velocity of the responses were extracted. Significant differences were found between the peak velocity in accommodation computed by fitting an exponential function and smoothing the experimental data (mean difference 2.36 D/s). Regarding disaccommodation, significant differences were found between latency and peak velocity, calculated with the two same strategies (mean difference of 0.15 s and -3.56 D/s, resp.). The strategy used to analyze accommodation and disaccommodation responses seems to affect the parameters that describe accommodation and disaccommodation dynamics. These results highlight the importance of choosing the most adequate analysis strategy in each individual to obtain the parameters that characterize accommodation and disaccommodation dynamics.

In vivo OCT assessment of anterior segment central axial lengths with accommodation.

PURPOSE: To assess changes in anatomic structures in the anterior eye segment in terms of axial lengths with accommodation via optical coherence tomography. METHODS: In this observational study, 25 eyes of 25 healthy adults were examined using the Visante® omni optical coherence tomography system. Central corneal thickness, anterior chamber depth, central lens thickness, and anterior segment length were assessed. The evaluated parameters were obtained with accommodation using different stimulus vergences, namely 0.0, -1.0, -2.0, and -3.0 D. Variation of these parameters was compared among different levels of accommodation. RESULTS: Central corneal thickness was not altered at any stimulus vergence during accommodation (p>0.05). Conversely, anterior chamber depth was significantly reduced (p<0.05), whereas central lens thickness was significantly increased (p<0.05). Anterior segment length also increased with accommodation (p<0.05), indicating backward movement of the posterior pole. CONCLUSIONS: There are significant variations in anterior segment lengths that occur with accommodation. Studying these changes will provide useful information regarding the accommodation mechanism that can improve our understanding of this process and facilitate clinical decision-making by practitioners.

In vivo OCT assessment of anterior segment central axial lengths with accommodation / Avaliação por OCT in vivo do comprimentos axiais centrais do segmento anterior

ABSTRACT Purpose: To assess changes in anatomic structures in the anterior eye segment in terms of axial lengths with accommodation via optical coherence tomography. Methods: In this observational study, 25 eyes of 25 healthy adults were examined using the Visante® omni optical coherence tomography system. Central corneal thickness, anterior chamber depth, central lens thickness, and anterior segment length were assessed. The evaluated parameters were obtained with accommodation using different stimulus vergences, namely 0.0, -1.0, -2.0, and -3.0 D. Variation of these parameters was compared among different levels of accommodation. Results: Central corneal thickness was not altered at any stimulus vergence during accommodation (p>0.05). Conversely, anterior chamber depth was significantly reduced (p<0.05), whereas central lens thickness was significantly increased (p<0.05). Anterior segment length also increased with accommodation (p<0.05), indicating backward movement of the posterior pole. Conclusions: There are significant variations in anterior segment lengths that occur with accommodation. Studying these changes will provide useful information regarding the accommodation mechanism that can improve our understanding of this process and facilitate clinical decision-making by practitioners.

RESUMO Objetivo: Avaliar as mudanças das estruturas anatômicas no segmento anterior do olho em termos de comprimentos axiais com acomodação por meio da tomografia de coerência óptica. Métodos: Neste estudo observacional, foram incluídos 25 olhos de vinte e cinco adultos saudáveis e medidos com o sistema Visante® omni tomografia de coerência óptica. A espessura corneana central, a profundidade da câmara anterior, a espessura central da lente e o comprimento do segmento anterior foram avaliados. Os parâmetros avaliados foram obtidos com acomodação usando diferentes vergências de estímulo: 0,0, -1,0, -2,0 e -3,0 D. A variação desses parâmetros foi comparada para os diferentes níveis de acomodação. Resultados: A espessura corneana central não foi alterada em nenhum estímulo durante a acomodação (p>0,05). A ACD mostrou uma redução significativa (p<0,05), enquanto a espessura central da lente foi significativamente aumentada (p<0,05). O comprimento do segmento anterior também aumentou com acomodação (p<0,05) indicando um movimento do polo posterior para trás. Conclusões: Há variações significativas nos comprimentos do segmento anterior que ocorrem com acomodação. Estudar essas mudanças fornece informações úteis sobre o mecanismo de acomodação para os profissionais, a fim de obter uma melhor compreensão desse processo e ajudá-los a tomar suas decisões clínicas.

Accommodative Stimulus-Response Curve with Emoji Symbols.

PURPOSE: To evaluate the static measurement of the accommodative stimulus-response curve with emoji symbols. METHODS: The accommodative stimulus-response curve was measured in 18 subjects using a Hartmann-Shack sensor to obtain the objective accommodative response from the Zernike defocus term. Measurements were acquired at different accommodative demands, from 0 to 3 D with a step of 0.5 D. Detailed and nondetailed emoji targets were used with two different sizes, corresponding to the two most common visual angles used in smartphones. RESULTS: A regression analysis was performed to fit the mean results obtained for each target. The determination coefficient was R2 ≥ 0.988 for all targets. For the detailed targets, the slopes for the averaged stimulus-response curve were 0.65 and 0.66 for the bigger and smaller sizes, respectively. For the nondetailed targets, the slopes were 0.60 and 0.58 for the bigger and smaller sizes, respectively. p values for these slopes were statistically significant for the two types of targets (p < 0.01). CONCLUSIONS: Our results reveal that the replacement of a word or several words by detailed or nondetailed emoji symbols seems not to provoke a different accommodative response in normal subjects and under standard viewing conditions in the use of smartphones.

Evaluation of the iridocorneal angle with accommodation using optical coherence tomography.

The changes in the iridocorneal angle structure during accommodation are assessed by means of anterior segment optical coherence tomography. Thirteen right eyes were included in the study. The device used for the measurement was the Visante®omni system. The stimuli were set up at different vergences (0.0 D, -1.5 D, and -3.0 D). The angle opening distance 500 and 750, the trabecular iris space area 500 and 750, and the scleral spur angle parameters were assessed at the nasal and temporal regions. The results in the iridotrabecular angle comparing the three accommodative states of the eye did not yield any statistically significant difference at nasal or temporal angle sections. In light of our results and in the conditions of our study, the structures of the iridocorneal angle are not significantly changed with accommodation.